1. Field of the Invention
The present invention relates to an oscillator wafer-level-package (WLP) structure and a method for the same, particularly to a TSV-based oscillator WLP structure having cap and base made of an identical material and a method for fabricating the same.
2. Description of the Related Art
Featuring stable piezoelectricity, quartz elements can precisely provide functions of reference frequencies, clock control, timing, and noise filtering in a wide range. Besides, some quartz elements are used to sense movement and pressure, and some are used as optical elements. Therefore, quartz elements are indispensables for electronics.
Many prior arts have proposed a lot of schemes for packaging quartz oscillators. A U.S. Pat. No. 5,030,875 disclosed a “Sacrificial Quartz-Crystal Mount”, which belongs to an early package technology using metal caps. The prior art has a complicated structure and is hard to reduce the package volume. A U.S. Pat. No. 6,545,392 disclosed a “Package Structure for a Piezoelectric Resonator”, wherein a package structure for a piezoelectric resonator includes a base which has a shape of flat box and made of an insulating material, and a thin lid bonded to the upper side of the base. A tuning fork type quartz crystal resonator piece is mounted at its one end, that is its base end, on electrode pads provided on the mounting surface in a cantilever manner using conductive adhesive so that it is parallel to the mounting surface, and hermetically sealed in a package with the lid engaged therewith. Either one or both of the mounting surface of the base and the inner surface of the lid has a recess formed at the location adjacent to the free end of a tuning fork type quartz crystal resonator piece so that the free end does not touch the inside surfaces of the packages when the quartz crystal resonator piece is largely dislocated on external impact. However, the prior art is expensive and hard to reduce the package size.
A U.S. Pat. No. 6,531,807 disclosed a “Piezoelectric Device”, wherein a package has a first region and a second region on one principal plane, and has a base including a ceramic board where wiring patterns to connect a quartz crystal resonator element and an IC chip for its driving are formed. In the base, a first sidewall enclosing the first region is arranged on the top side of the board, and the quartz crystal resonator element is mounted in a first void space delimited in its internal, and the IC chip is mounted in a second void space delimited by a second sidewall enclosing the second region. The first sidewall is formed to be higher than the second sidewall, a metal cover is seam welded at the upper end thereof, and the first void space is sealed in a vacuum or nitrogen atmosphere. The IC chip of the second region is resin sealed. In addition to the miniaturization, thinning and high-accuracy frequency adjustment, the present invention reduces or eliminates the stray capacity caused by the adsorption of gas that is generated from electronic components and wiring, package/wiring structure, and the like to reduce or prevent the reduction of variable amount of frequency and displays a high frequency stability and aging characteristics. It is particularly suited to a high-frequency oscillator with a large variable amount of frequency. Since the prior art arranges the resonator element and the IC chip in different regions and uses a ceramic base as the package substrate, it has a large area and a high fabrication cost.
A U.S. Pat. No. 7,098,580 disclosed a “Piezoelectric Oscillator”, wherein a quartz-crystal oscillator has a configuration wherein a rectangular container accommodating a piezoelectric oscillator device therein is fixed to a rectangular supporting substrate on which an IC device is mounted via spacer members formed of metal bodies. On the surface of the supporting substrate, part or all of the IC device and side faces of the spacer members are coated with a resin material. When the quartz-crystal oscillator is implemented on a main board by soldering or the like, the problem that the solder for bonding the quartz-crystal oscillator to the main board is adhered to the spacer members, thereby causing a short-circuit can be effectively prevented. However, the prior art cannot effectively reduce the overall volume. Also, the prior art has a higher fabrication cost.
A U.S. Pat. No. 7,608,986 disclosed a “Quartz Crystal Resonator”, wherein a quartz crystal resonator includes a quartz crystal resonator element having a main surface including an X axis (electrical axis) and a Z′ axis of an inclination rotated at an angle (y) equal to or greater than 36.4 degrees and equal to or smaller than, 40.5 degrees from a Z axis (optical axis) around the X axis, a main vibrating portion vibrating at a predetermined resonance frequency (f) and a supporting portion integrally formed with the main vibrating portion in such a manner as to be formed peripherally to surround the main vibrating portion, and two covers having a thermal expansion coefficient equal to or greater than 6.times.10.sup.-6 per degrees centigrade and equal to or smaller than 10.times.10.sup.-6 per degrees centigrade and bonded to the supporting portion so as to sandwich the quartz crystal resonator element therebetween. The prior art forms a sandwich structure, wherein the substrate and the quartz crystal resonator element respectively have different thermal expansion coefficients. Temperature variation would induce thermal stress in the quartz crystal resonator element and causes deviation of the vibration frequency. Therefore, the prior art has to use a quartz chip cut at special angles and adopt a cap and a base respectively having special thermal expansion coefficients. Therefore, the prior art has a complicated fabrication process and a high fabrication cost.
All the abovementioned prior arts are beset by the plight of having to use ceramic substrates. Therefore, the products of the prior arts are expensive, and the raw materials thereof are likely to run out of stock. Further, the thermal stress of the sandwich structure is still hard to overcome at present.
Therefore, the manufacturers in the field are eager to develop a novel oscillator package structure to overcome the abovementioned problems.